This invention relates to test structures for semiconductor fabrication, and more particularly to probe-able voltage contrast test structures for electrical testing and voltage contrast inspection, and a method for detecting defects using the same.
Mask area (space on the reticle) is a precious resource used during technology development and manufacturing of integrated circuits. Mask sets may cost 1 million dollars or more. During process development a wide range of test structures for characterizing the yield and functionality of different circuit components must incorporated on each mask set. In addition, design IP must also be included to test out the building blocks for ICs that will be manufacturing for sale. During manufacturing, primarily chips that will be sold consume the entire mask area. Generally there is not enough room on a mask set to accommodate all the test structures and other designs that could provide value Two classes of test structures often included on mask sets are probe-able test structures (e.g., combs and serpentine patterns) which are used to test for shorts and opens using electrical probes, and voltage contrast test structures which are used in line with a scanning electron microscope (SEM). The voltage contrast test structures provide feedback on defectivity at a level shortly after defect formation. The exact location of each defect is also isolated using this technique. Probe-able test structures are important because they enable a very large area to be tested quickly. Voltage contrast inspection is time consuming and so many wafers go without inspection. A greater number of wafers can be probed. Also using electrical probes, the exact resistance can be measured.
Probe-able test structures and voltage contrast test structures are different in structure. Probe-able test structures require large probe pads, which are connect to two or more electrical nodes in the structure. FIGS. 1A and 1B are diagrams illustrating conventional probe-able comb and serpentine structures, respectively. As shown in FIG. 1A, a conventional probe-able comb test structure 100 is provided. The conventional probe-able comb test structure 100 includes a plurality of probe pads 101 and 102 respectively connected to comb-like structures 103 and 104. In FIG. 1B, a conventional probe-able serpentine test structure 110 is provided. The conventional probe-able serpentine test structure 110, includes a plurality of probe pads 111 and 112 and a single meandering metal or wire 113 connected therebetween.
On the other hand, a voltage contrast test structure requires smaller electrical nodes for efficient defect isolation. FIG. 2 illustrates a conventional voltage contrast test structure 200. The conventional voltage contrast test structure 200 includes a grounded comb 201 including a plurality of grounded tines 202, and a plurality of floating tines 203 where each floating tine 203 is in between each grounded tine 202. These floating tines 203 are independent to allow defect isolation. To test for a short, end portions of the floating tines 203 are scanned in a scan area 204 and if there is a bridge from any one of the floating tines 203 to any of the grounded tines 202, the respective floating tine 203 becomes grounded.
The masking area has a limited amount of space. The probe-able test structures and the voltage contrast test structure typically are allocated in separate areas since they are designed differently. Therefore, a large amount of space within the masking area is used to accommodate these test structures.